Monjurosuchus

''Monjurosuchus'' is a genus of choristoderan reptile that lived in what is now China and Japan during the Early Cretaceous. It has large eyes, a rounded skull, robust legs with short claws, and a long, thin tail. Fossils have been found that preserve soft tissue, showing that it had soft skin and webbed feet.

Description and history

''Monjurosuchus'' was first found in China as part of the Early Cretaceous Jehol Biota. Named in 1940, the type species ''M. splendens'' was the first reptile described from the Yixian Formation. The holotype specimen was lost during World War II but was replaced in 2000 by a recently discovered neotype preserving soft tissue. In 2007, remains were described from the Okurodani Formation of the Tetori Group of Japan. The Japanese material represents a different species of ''Monjurosuchus'' that has not yet been named.

''Monjurosuchus'' was a small choristodere, reaching a length of 40 cm with a 5 cm skull. Unlike related choristoderes, ''Monjurosuchus'' has a relatively short neck with eight vertebrae, one less than usual. The skull is rounded rather than pointed and is dorsoventrally flattened in all fossils. The eye sockets are large and prominent temporal regions extend from the back of the skull. The jaws are lined with small, sharp teeth, while the palate is covered in closely spaced tooth batteries. One distinguishing feature of ''Monjurosuchus'' is the lack of a lower temporal fenestra, a hole in the back of the skull that is common in many other diapsid reptiles, including most choristoderes. ''Monjurosuchus'' is also distinct in having small spikes on the edge of the squamosal bone at the back of the skull.

Specimens from China preserve soft tissue, including scales and webbing between the toes of the feet. The scales of ''Monjurosuchus'' were small, giving the animal soft skin. Two rows of larger scutes run along its back. The rest of the scales on the back are small, while the scales on the underside are slightly smaller. The skin of ''Monjurosuchus'' has a similar appearance to the living Chinese crocodile lizard ''Shinisaurus''.

The feet of ''Monjurosuchus'' are webbed, with skin covering all parts of the foot but the short claws. The limbs were robust and the hips are wide. The long, slender tail shows no adaptations for its presumed semi-aquatic lifestyle. Gastralia are present on the underside of ''Monjurosuchus'' and are much thinner than the ribs. Intestinal contents are preserved between the gastralia and ribs of one specimen. Most of the material is sediment, but there are also fragments of what may be arthropod cuticle, indicating that ''Monjurosuchus'' may have fed on invertebrates.

Classification

''Monjurosuchus'' is a basal choristodere that lies outside the more advanced Neochoristodera. When named in 1940, it was placed in its own family Monjurosuchidae. Unlike ''Monjurosuchus'', neochoristoderes have small, dorsally facing eyes and long snouts. ''Philydrosaurus'', another Early Cretaceous Chinese choristodere, was grouped with ''Monjurosuchus'' in Monjurosuchidae. A 2007 phylogenetic analysis of choristoderes found only weak support for this family, as ''Philydrosaurus'' seemed to be a more basal choristodere than ''Monjurosuchus''. A close relationship was found between ''Monjurosuchus'' and the Miocene ''Lazarussuchus'', but this was only weakly supported.

Phylogeny from the analysis of Dong and colleagues (2020):

References

{{Taxonbar, from=Q3010132

Choristodera
Early Cretaceous reptiles of Asia
Yixian fauna
Prehistoric reptile genera